Recent seatbelt retractors additionally include a pretensioner adapted to instantly wind up a belt upon a vehicle collision and effectively restrain the body of an occupant and a force limiter mechanism adapted to reel out the belt wedding while absorbing energy if a set load or higher is applied on the belt which has the effect of reducing a load upon the chest of the occupant. An example of such that the device is provided by referenced to PCT Application No. 2003-502204.
As shown in FIG. 10 appended to this specification, a seatbelt retractor disclosed in PCT Application No. 2003-502205 includes a force limiter mechanism in which a torsion bar (twist bar) 213 absorbs energy as the bar is twisted and plastically deforms, so that the belt is unreeled for a prescribed amount. The torsion bar 213 has a section 214 having a larger cross section and a section 215 having a smaller cross section and includes connecting pieces 216a and 216b at intermediate parts of the sections 214 and 215 and one end of the torsion bar 213. The connection piece 216b is coupled to a spindle (belt shaft) 212, and the connection piece 216a is coupled to a torque tube (torque pipe) 218. The torsion bar 213 is connected to a tread head (profile head) 250 at the other end.
The force limiter mechanism includes a switching mechanism that switches energy absorption from a high force level to a low force level. As shown in FIG. 11, the switching mechanism carries out energy absorption in a high force level to the section 214 of the torsion bar 213 through the torque tube 218 from a spindle 212 while a locking element (nail) 221 couples the spindle 212 and the torque tube 218. When the locking element 221 is detached from the torque tube 218, the section 215 of the torsion bar 213 is twisted from the spindle 212, and energy absorption in a low force level is carried out.
The locking element 221 is swingably supported around a rotation center 222 in a notch 240 formed at a cross section of the spindle 212. The locking element 221 is held in engagement with the torque tube 218 while the outer circumferential side thereof is surrounded by a spindle ring (shaft ring) 245. When the spindle ring 245 is moved in the axial line direction, the locking element 221 is released from the support 224 of the spindle ring 245 and swings outward in the notch 240, so that the spindle 212 and the torsion bar 213 are detached from each other.
6As shown in FIG. 12, a driving device 226 having a pyrotechnic filler 227 is provided in the cover 220 of a belt winding-up device 210, and the filler 227 functions to linearly move a piston 228. The piston 228 makes an access to a step 229 that radially protrudes from a switch ring (operation ring) 219, which rotates the switch ring 219, and the rotation pushes and moves the spindle ring 245 away from the cover 220 in the axial line direction.
In the switching mechanism of the force limiter mechanism disclosed in PCT Application No. 2003-502204, the switch ring 219 is driven to rotate by the activation of the piston 228 in a stable manner by setting strict dimensional tolerances for the piston 228 and the switch ring 219 themselves and their peripherals. Therefore, strict dimension management is necessary in the switching mechanism, which increases the cost.
The present invention is in view of the problem and it is an object of the present invention to provide a seatbelt retractor that allows the switching mechanism of the force limiter mechanism to have improved operation stability while achieving cost reduction.
The object of the present invention is achieved by the following configurations.
A seatbelt retractor including a retractor frame, a spindle rotatably supported at the retractor frame and capable of winding up a seatbelt therearound, a torsion bar provided in the spindle and having one end coupled to the spindle and a plurality of shaft parts having different torsional torque characteristics, an emergency locking mechanism capable of locking rotation of the spindle by locking the other end of the torsion bar, a torque tube coupled to the torsion bar between the plurality of shaft parts and provided in the spindle, and a switching mechanism implementing switching between a state in which the torque tube rotates together with the spindle and a state in which the torque tube rotates relatively to the spindle, the switching mechanism includes a locking mechanism locking the torque tube with respect to the spindle so that the torque tube rotates together with the spindle, a switching member capable of rotating to unlock the locking mechanism, and a housing storing the switching member, a driving member adapted to activate the switching member, and a gas generator that generates gas for pushing out the driving member upon activation of the switching mechanism, and the housing of the switching mechanism has a protrusion that protrudes in an incoming direction of the switching member at an abutment part hit by the switching member when the switching member is rotated by the driving member.
In a further embodiment the seatbelt retractor described above in which the protrusion deforms when the switching member hits the protrusion.
In a still further embodiment is seatbelt retractor described previously in which the locking mechanism includes a locking member attached on the spindle side in a through hole provided radially through the spindle and rotatable between a locking position in which the torque tube is locked with respect to the spindle so that the torque tube rotates together with the spindle and an unlocking position in which the torque tube is unlocked from the spindle so that the torque tube rotates relatively to the spindle, and a restriction ring radially abutting against the locking member to restrict the locking member in the locking position, the switching member is a switch ring having an operated part that is movable axially from a position, in which the restriction ring abuts against the locking member, to a position apart from the locking member and that is allowed to protrude radially and hit the protrusion at the abutment part, and the protrusion extends axially to protrude in the incoming direction of the switching member.
In a still further embodiment is the seatbelt retractor described previously in which the housing of the switching mechanism includes a plurality of ramp surfaces inclined in a moving direction of the switch ring at a sliding surface on which the switch ring slides, and the switch ring moves axially by sliding along the plurality of ramp surfaces while rotating in a circumferential direction by activation of the driving member.
In the seatbelt retractor according to the present invention, the housing of the switching mechanism has the protrusion that protrudes in an incoming direction of the switching member at an abutment part hit by the switching member when the switching member is rotated by the driving member. In this way, the switching member activated by the driving member is restricted from axially shifting by the protrusion of the housing and operates stably, so that the switching mechanism of the force limiter mechanism may have improved operation stability while achieving cost reduction.